= Gravitational memory
<Gravitational memory> is a persistent change in the relative configuration of freely falling bodies after a gravitational-wave burst has passed. In the weak-field transverse-traceless description, an initially separated pair obeys $\Delta\xi^i\simeq\tfrac12\Delta h^{\mathrm{TT}}_{ij}\xi^j$. A nonzero net strain change leaves a displacement rather than only a temporary oscillation.
Memory can arise from changes in the motion of material sources and from the <energy> carried away by <radiation> itself. The latter contribution reflects the nonlinear gravitational role of <wave> <energy>. Distinguishing this slow or step-like response from detector drift requires more than identifying an oscillatory waveform.<Gravitational Memory, BMS Supertranslations and Soft Theorems by Andrew Strominger and Alexander Zhiboedov>[Introduction and Section 4.2, inertial detector displacement memory]{ref}
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